Deflecting coils for cathode ray tubes



July 7, 1964 TOSHIO IMANAKA DEFLECTING cons FOR CATHODE RAY "mass 1N VHV TOR.

United States Patent DEF LECTING COILS FOR CATHODE RAY TUBES Toshlo Imanaka, Takatsuki-shi, Japan, assignor to Matsushita Electric Industrial Co., Ltd., Osaka, Japan, a

corporation of Japan Filed Nov. 28, 1960, Ser. No. 71,975 Claims priority, application Japan Dec. 23, 1959 3 Claims. (Cl. 317-200) This invention relates to improvements in deflecting coils for cathode ray tubes.

An object of the present invention is to provide deflecting coils of the kind specified in which deleterious deformation of magnetic lines due to pulse voltages of horizontal deflecting coils is prevented.

Another object of the present invention is to provide deflecting coils of the kind specified with maximum space factor.

A further object of the present invention is to provide deflecting coils of the kind specified which produce uniform deflecting magnetic fields.

Other objects and features of the present invention will be made obvious from the following detailed description when read with reference to the accompanying drawings, in which FIG. 1 shows a cross-sectional view of a conventional deflecting coil;

FIGS. 2 and 3 are the equivalent circuit diagrams of two types of conventional deflecting coils;

FIG. 4 is an equivalent circuit diagram of a deflecting coil according to the present invention; and

FIG. 5 is a perspective view of a deflecting coil according to the present invention.

In the vertical deflecting coil of a cathode ray tube, a resonant circuit is formed by upper and lower layers of turns of the' conductor and the distributed capacities between the turns. This resonant circuit is excited to oscillate by saw-toothed voltage pulses of the horizontal deflecting coil. These oscillations cause deleterious deformation of magnetic field generated by the vertical deflecting coil.

In order to overcome the above-mentioned disadvantage, it has been proposed to wind around a magnetizable core multiple layers of turns in one and the same helical direction. However, in one of the known types, such as disclosed in German patent specification No. 720,123, the deflecting coil has substantially a rectangular cross section, with equal number of turns in all of the layers and uniform distribution of turns in each layer, so that a uniform deflecting magnetic field cannot be produced. Furthermore when the horizontal deflecting coil is wound, the space factor is very low and the efficiency is lowered.

In another known type of deflecting coil, provision is made for overcoming the disadvantages of the abovementioned German patent, but such a provision is too complicated and impractical to be adopted for conventional deflecting coils.

According to the present invention, all the layers of conductor turns forming a deflecting coil are wound in one and the same helical direction, and at the same time, the distribution of turns in each layer is so graduated that the turns are closest at the center and most coarse at the outer ends. In other words, the density of turns decreases as the winding progresses from the center to the ends. With this arrangement, the present invention has succeeded in substantially overcoming the aboveoutlined disadvantages of known devices.

Referring to FIG. 1 an oxide core 1 has a vertical deflecting coil 2 of concentrated winding wound about it. The coil 2 may alternatively have a winding distri- 3,140,432 Patented July 7, 1964 bution as shown at 3. Distributed horizontal deflecting coils 4 and 5 are wound against the inner surface of oxide core 1. The horizontal and vertical deflecting coils are separated from each other by an insulating frame 6. As is shown in FIG. 1, when the horizontal deflecting coils 4 and 5 are distributively wound according to the formula cos 0--cos 0, and the vertical deflecting coil is a concentrated winding of rectangular crosssection, there is formed a vacant space 7 which lowers the efliciency in proportion to the cross-sectional area of the space 7. For this reason and also in order to obtain an uniform deflecting magnetic field, it is desirable to employ the vertical deflecting coil having a distributed winding.

However, it is not desirable to carry out the distributed winding by merely changing the number of turns of each layer as in the prior art. In this connection, there should be considered the equivalent circuit of the vertical deflecting coil when excited by the horizontal pulses. Referring to FIG. 2, when the vertical deflecting coil comprises two layers 11 and 12 of an equal number of turns wound in one and the same helical direction, the deflecting magnetic fields produced thereby are cumulative. However, the equivalent circuit excited by horizontal deflecting pulses comprises winding 11, distributed capacitance 13, winding 12 and distributed capacitance 14. The horizontal deflecting pulses produce voltages of equal magnitude but of opposite directions in windings 11 and 12. Consequently, the equivalent circuit accordingly has no effective inductance but only resistance and capacitance and hence does not oscillate.

In FIG. 3, the vertical deflecting coil comprises two layers 21 and 22 of distributed windings of different numbers of turns wound in one and the same helical direction. Electric current for producing the deflecting magnetic field flows through respective portions 212, 211, and 213 of the winding 21 to the winding 22. Accordingly, the deflecting magnetic fields produced by the windings 21 and 22 are cumulative. In considering the excitation by the horizontal deflecting pulses, the winding 21, distributed capacitance 23, winding 22, and distributed capacitance 24 comprise a circuit quite similar to that of FIG. 2 and no oscillations are generated. However, winding section 212 and distributed capacitance 26, and winding section 213 and distributed capacitance 25 form an oscillating circuit having inductance, capacitance and resistance. If the overall inductance is of the order of 1 henry, an oscillation of about 200 kc. is produced which causes distortion of images of the cathode ray tube.

Now, according to the present invention, as diagrammatically shown in FIG. 4, two layers 31 and 32 of equal numbers of turns are wound in one and the same helical direction. However, the distribution of turns in each layer is not uniform throughout, the turns being closest at the central portions, as shown in layer 31 at 35, and the winding pitch being gradually greater towards the opposite ends. With such an arrangement, due to distributed capacitances 33 and 34, the excitation by the horizontal deflecting pulses is same with the case of FIG. 2, and no oscillations are produced. However, at the same time, since the manner of distribution is similar to the case of FIG. 3, a uniform deflecting magnetic field is obtained.

In FIG. 5, a deflecting coil 41 embodying the present invention is wound around a magnetizable core 40. The coil 41 includes sixteen layers each having turns of conductor. For simplicity only the first layer is shown having been completed and the conductor having been brought to the starting end of winding of the second layer.

The total number of turns of the coil 41 is l80 l6=2880. When this deflecting coil Was used in a practical cathode ray tube, there was not observed any appreciable distortion of the image due to the horizontal deflecting pulses. The efficiency of this deflecting coil was 1.4 times that of rectangular cross-section, and 2.3 times that of saddle type. It also produced a uniformly distributed magnetic field. In addition, deflecting coils according to the present invention are very economical in manufacture in comparison to those of the prior art.

I claim:

1. A deflecting coil for a cathode ray tube comprising an arcuate shaped magnetizable core and a plurality of superposed layers of turns toroidally wound about said magnetizable core starting at one end of said core and ending at the other end of said core, all of said layers having an equal number of turns Wound in one and the same helical direction throughout the winding and extending over the same extent, the turns in each of said layers being closest at the central portion and gradually coarser towards the opposite ends of said layer.

2. A vertical deflecting coil for a cathode ray tube which is substantially immune to oscillations induced by horizontal deflection pulses comprising an arcuate shaped core of magnetizable material, said arcuate shaped core including a central portion and first and second end portions, and a plurality of layers of conductor windings, each of said layers of conductor windings including an equal number of conductor turns toroidally wound about said arcuate shaped core and having a start at the first end portion of said arcuate shaped core and an end at the second end portion of said arcuate shaped core so that the conductor turns in each layer have the same helical direction throughout each conductor winding and each conductor winding extends over the same length of said arcuate shaped core, and the turn density of the turns of each of said conductor windings per unit length of said arcuate shaped core gradually and uniformly decreased from a maximum value at the central portion of said arcuate shaped core to the same minimum value at the first and second end portions of said arcuate shaped core.

3. The vertical deflecting coil of claim 2 wherein the end of one conductor winding at the second end portion of said arcuate shaped core is connected to start of an adjacent conductor winding at the first end portion of said arcuate shaped core whereby said conductor Windings are serially connected and cooperate to cancel inductances susceptible to excitation by horizontal voltage pulses for suppressing undesirable oscillations.

References Cited in the file of this patent UNITED STATES PATENTS 2,830,212 Hanlet Apr. 8, 1958 2,926,273 Haupt et al Feb. 23, 1960 3,007,087 Corpew Oct. 31, 1961 3,094,649 Marley June 18, 1963 

1. A DEFLECTING COIL FOR A CATHODE RAY TUBE COMPRISING AN ARCUATE SHAPED MAGNETIZABLE CORE AND A PLURALITY OF SUPERPOSED LAYERS OF TURNS TOROIDALLY WOUND ABOUT SAID MAGNETIZABLE CORE STARTING AT ONE END OF SAID CORE AND ENDING AT THE OTHER END OF SAID CORE, ALL OF SAID LAYERS HAVING AN EQUAL NUMBER OF TURNS WOUND IN ONE AND THE SAME HELICAL DIRECTION THROUGHOUT THE WINDING AND EXTENDING OVER THE SAME EXTENT, THE TURNS IN EACH OF SAID LAYERS BEING CLOSEST AT THE CENTRAL PORTION AND GRADUALLY COARSER TOWARDS THE OPPOSITE ENDS OF SAID LAYER. 